Make Herald Rules sticky in X-Herald-Rules

Summary:
See T354. List every rule which has ever been applied in X-Herald-Rules, not
just the ones which most recently triggered.

Also some random fixes while I was debugging this:

• When conduit methods throw non-conduit exceptions, make sure they get

logged.

• Trigger the Facebook "tasks" backcompat block only if we were going to fail

(this should reduce the shakniess of the transition).

• Fix some log spew from the new field stuff.

Test Plan:

• Created a rule (ID #3) "No Zebras" which triggers for revisions without

"zebra" in the title.

• Created a revision without "zebra" in the title, got X-Herald-Rules: <2>,

<3>

• Updated revision to have "zebra" in the title, verified rule did not trigger

in Herald transcript.

• Verified X-Herald-Rules is still: <2>, <3>

Reviewed By: aran
Reviewers: aran, jungejason, tuomaspelkonen
CC: aran, epriestley
Differential Revision: 817